Study Finds That Earth-Like Planets Could Have Too Much Water For Life

There has been much excitement over the discovery of the Earth-like planet Proxima b, orbiting our nearest neighboring star Proxima Centauri. The planet, discovered earlier this year via its gravitational influence on its star, sits in the star's habitable zone, the small range of orbit wherein we believe life might be possible.

But we still don't know much about what Proxima b is like—for all we know, it's a barren radiated hellscape of rocks without any of the necessities for life. A new study from the University of Bern, to be published in the journal Astronomy and Astrophysics, looked at the likelihood that planets like Proxima b could contain liquid water and came to some surprising conclusions.

First off, the planetary evolution models the scientists created showed that there are many Earth-sized rocky planets floating in the habitable areas around distant stars. "Our models succeed in reproducing planets that are similar in terms of mass and period to the ones observed recently," Yann Alibert, of the Center of Space and Habitability (CSH) at the University of Bern, said in a statement. "Interestingly, we find that planets in close-in orbits around these type of stars are of small sizes. Typically, they range between 0.5 and 1.5 Earth radii with a peak at about 1.0 Earth radius."

The fact that many Earth-sized planets are in close orbit around stars like our own is a good sign for finding life. The study also predicted that many of these planets could contain a lot of liquid water. Maybe even too much. In 90 percent of the exoplanets simulated by the study, their mass consisted of more than 10 percent water. Earth is only 0.2 percent water, meaning that these simulated planets would have exponentially more water than we do on Earth. This might not be a good thing for the possibility of life.

"While liquid water is generally thought to be an essential ingredient, too much of a good thing may be bad," Willy Benz, the study's co-author, said. Previous studies have shown that planets composed of such a high percentage of water have trouble controlling their climates, which is an unfavorable trait for life to develop. The closeness of planets like Proxima b to their stars also means they may be highly irradiated, so it's possible that any life would need to hide deep behind layers of ice.

"Habitable or not, the study of planets orbiting very low mass stars will likely bring exciting new results, improving our knowledge of planet formation, evolution, and potential habitability," Benz says. And on the plus side, there are so many millions of these planets, its hard to imagine life doesn't exist out there on one of them.

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